Vacuum processing systems for processing 100 mm, 200 mm, 300 mm or other diameter wafers are generally known. Examples include the CENTURA.RTM. and ENDURA.RTM. platforms available from Applied Materials, Inc. in Santa Clara, Calif. An example of a typical vacuum processing system 100 is shown in FIG. 1. The system 100 typically has a centralized transfer chamber 102 (shown in detail in FIG. 2) mounted on a monolith platform (not shown). The transfer chamber 102 is the center of activity for the movement of wafers being processed in the system. One or more process chambers 104 and one or more load locks 108 attach to the transfer chamber 102 at its various facets 106, 112. Elongated apertures commonly known as slit valve apertures 14 (shown in FIG. 2) provide a transfer plane between the process chambers 104 and the load lock chambers 108 through which the wafers are passed. The wafers are transferred by a robot 120 disposed in the transfer chamber 102. The apertures 14 are selectively opened and closed to isolate the process chambers 104 from the transfer chamber 102 while wafers are being processed in the process chambers 104. The process chambers 104 are either supported by the transfer chamber 102 and its platform or by their own platform.
Referring briefly to FIG. 2, a perspective view is shown of the transfer chamber 102 with the lid and the robot 120 removed so that the interior of the transfer chamber 102 is visible. A centrally located orifice 66 formed in a floor 62 provides a means for mounting the robot 120 therein. Openings 38 formed in the floor 62 are adapted to receive slit valve apparatuses (discussed in detail below) therethrough. As discussed above, the slit valve apertures 14 formed in the facets 106 provide a transfer plane between the transfer chamber 102 and the process chambers 104 (shown in FIG. 1).
While the transfer chamber 102 is typically held at a constant vacuum, the process chambers 104 may be pumped to a greater vacuum or backfilled with gases to increase the pressure therein in preparation for performing their respective processes. The process chambers 104 may perform various processes such as rapid thermal processing, physical vapor deposition, chemical vapor deposition, etching, etc. After processing, the relative pressures of the process chambers 104 and the transfer chamber 102 are equalized before opening the valve to permit fluid communication between the chambers.
Referring again to FIG. 1, a mini-environment, or wafer handling chamber 114, which attaches to the load lock chambers 108 is shown. A wafer aligner 119 is disposed within the mini-environment 114 so that it is substantially in or near the pathway of a wafer being moved from a pod loader 115-118 to a load lock chamber 108. The wafer aligner 119 centers the wafers and orients the direction of the wafers according to the requirements of a process that the wafers are to undergo in the process chambers 104. An example of a wafer aligner 119 is the PRE 200 Series Wafer Pre-Aligner available from Equipe Technologies of Sunnyvale, Calif. One or more robots 124, 125 are disposed within the mini-environment 114 for transferring the wafers between pod loaders 115-118, the wafer aligner 119, and the load lock chambers 108. An example of this type of robot 124, 125 is the ATM-105 available from Equipe Technologies of Sunnyvale, Calif.
As mentioned above, access between the load locks 108, the transfer chamber 102, and the process chambers 104 is provided through slit valve apertures 14 which are selectively sealed by a slit valve apparatus. FIG. 3 shows a typical slit valve apparatus 32 disposed in the transfer chamber 102. The slit valve apparatus 32 is shown disposed through the opening 38 and mounted to the transfer chamber floor 62 by a mounting bracket 52. The slit valve apparatus 32 generally includes a piston rod 36 having a first end disposed through a pneumatic cylinder 40 and a second end coupled to a door 28 by an adjustment mechanism 56. In order to maintain the extreme vacuum within the various environments of the system 100 (shown in FIG. 1), the slit valve door 28, having an O-ring 34 disposed thereon, must be hermetically sealed over the aperture 14. A seat 22 includes a seating surface 24 defining a sealing plane 26 which is angularly disposed with respect to the transfer plane 20 and perpendicular to the axis of actuation 54. In the closed position, the door 28 abuts the seating surface 24.
The slit valve apparatus 32 is activated by the injection of compressed air into an inlet/exhaust port 50 of the pneumatic cylinder 40. A constant psi of compressed air is supplied to the pneumatic cylinder 40 so that a terminal stroke velocity is reached prior to the sealing of the slit valve aperture 14. At the end of its stroke, the slit valve door 28 impacts the aperture 14 and halts the slit valve apparatus' stroke. Thus, the speed of the door 28 relative to the aperture 14 is abruptly terminated and the processing system 100 (shown in FIG. 1) as a whole absorbs the door's kinetic energy.
In an effort to increase throughput, the wafers being processed have become increasingly larger. The trend today is to use 300 mm wafers to form multiple devices thereon. Larger wafers, of course, require larger processing systems which include larger slit valve doors and apertures. Larger doors, in turn, require larger components such as the pneumatic cylinder, mounting bracket and adjustment mechanism. It has been discovered in the scale-up process for 300 mm substrates that increasing the slit valve components creates additional concerns. Since the door's kinetic energy and momentum is a function of it velocity and mass, an increase in mass results in increased kinetic energy and momentum for a given velocity. In general, total system vibration effects reach a critical level creating pervasive adverse conditions. For example, particle generation, metal to metal contact, hermetic sealing, door alignment, and pneumatic cylinder and door damage are significantly more problematic. Further, with larger slit valve doors the vibration is not localized to the immediate chamber area surrounding a particular slit valve. Rather, the force of impact affects remote parts of the chamber, thereby damaging delicate instrumentation and interfering with ongoing processes in other chambers. These undesirable conditions are caused primarily by the sealing impact of more massive slit valves.
There remains a need, therefore, for a slit valve apparatus and method which minimizes the total vacuum system trauma caused by impact of the slit valve door upon closing, thereby reducing the generation of particle debris, vibration, and damage to the vacuum system's components, including the pneumatic air cylinder.